1. Field of the Invention
The present invention relates to a fire sensing system using an infrared sensing process and more particularly to a fire sensing system separating an incident infrared radiation into a plurality of wavelength bands, sensing a change in the absolute value and the ratio of an infrared radiation of each separated wavelength band, and determining in response to the sensed time change whether a disastrous fire occurs or not. The present invention relates to a fire sensing system adapted for use in a fire prevention system used in a residence, a building, a warehouse, etc., requiring a reliable and highly sensitive fire sensing which is free from a false alarm caused by nondisastrous flaming sources such as an electric heater, a gas heater or a stove.
The present invention also relates to a technology used with an environment monitor sensing the occurrence of an indoor disastrous fire, and an indoor environment unpleasant to a person and produces a signal controlling an alarm or an air conditioner.
2. Description of the Related Art
A multitude of prior-art fire sensing methods and systems automatically sensing the occurrence of disastrous fire have been provided. These methods and systems intend to sense the occurrance of disastrous fire in a predetermined monitored area and must operate so that a malfunction due to a heating source providing no disastrous fire, e.g., a stove rarely occurs while maintaining a high sensitivity to the occurrence of a disastrous fire.
Prior-art fire sensing systems using, e.g., a phototube, bimetal or telecamera have been provided. The phototube type fire sensing system is subject to malfunction due to sunlight or light from an electric lamp, for example, because the phototube is sensitive to ultraviolet wavelengths. The bimetal type fire sensing system is insufficiently effective because of low fire-sensitivity of the bimetal. The telecamera type fire sensing system requires an excessive number of telecameras as well as a continuous monitoring by a person, so that a desired performance is difficultly obtained.
Recently, an infrared radiation sensing process for sensing an infrared radiant from a flame has been greater noticed. In this infrared radiation sensing process, both a simple system determining the occurrence of disastrous fire when it senses an infrared radiation of a predetermined level or higher and a fire sensing system (see Examined Japanese patent application publication No. SHO 56-7196) including a method of determining whether or not the level of an output signal from an infrared sensor tends to increase for a predetermined period of time or more have been proposed.
In addition, in order to increase reliability, efforts have been made in developing a technology of separately sensing two or more wavelength band of infrared radiation from a flame and of determining whether a disastrous fire occurs or not from sensed signal. One form of this technology is a system including a sensor for visible or near infrared radiation and a sensor for other infrared radiation, the system determining a nondisastrous fire when the intensity of the visible or near infrared radiation is stronger than that of the other infrared radiation such as the case of a radiation from am electric lamp, etc.
Another form of this technology is a system sensing the intrinsic spectral distribution of a flame. The spectral distribution of infrared radiation from an infrared source absent a flame, is generally in agreement with Planck's law of radiation as shown in solid lines A and C of FIG. 2 so that the higher the temperature of a heating object, the more the top of the spectral distribution shifts towards a shorter-wavelength band. On the other hand, an infrared radiant object with flame has a different intrinsic character. That is, it has a spectral distribution with a peak as shown in the solid line B of FIG. 2. The peak of the spectral distribution of the solid line B is derived from the phenomenon of CO.sub.2 -molecular resonance radiation at about 4.3 .mu.m wavelength. Thus, in principle, sensing a peak of about 4.3 .mu.m wavelength caused by CO.sub.2 -molecular resonance radiation senses a flame.
In order to sense the peak of about 4.3 .mu.m wavelength, some attempts have been proposed. For example, the art of Unexamined Japanese patent application publication No. SHO 50-2497 senses the amount of radiation at the 4.3 82 m wavelength and at two wavelengths before and after the 4.3 .mu.m wavelength and determines a presence of flame when each of the amounts of radiation at the 4.3 .mu.m wavelength and at the two wavelengths before and after the 4.3 .mu.m wavelength equals or exceeds a predetermined value. In addition, the art of Unexamined Japanese patent application publication No. SHO 57-96492 determines whether or not there is a depression between two projections in the amount of radiation in order to sense the occurrence of flame.
In accordance with a method of determining the occurrence of nondisastrous fire when the radiation intensity of visible or near infrared radiation is greater than the radiation intensity of the other infrared radiation as in light from an electric lamp, the occurrence of a false alarm due to a normal light from the electric lamp is rare. On the other hand, since this method determines as the occurrence of disastrous fire, the presence of a heater such as an electric heater, having no or low visible or near infrared radiation, the method produces a false alarm, so that an application of the method is very restricted.
In accordance with the method of sensing the amounts of radiation at the 4.3 .mu.m wavelength and two wavelengths before and after the 4.3 .mu.m wavelength and determining the presence of flame when each of the amounts of radiation at the 4.3 .mu.m wavelength and two wavelengths before and after the 4.3 .mu.m wavelength equals or exceeds the predetermined value, this method can sense the presence of flame but not determine whether the flame is derived from a disastrous fire or a normal or flame producing heater. That is, this method entails a drawback in that it can produce a false alarm in response to the occurrence of a flame of a gas range, gas stove or the like.
Various prior-art air conditioners sensing indoor conditions by means of a temperature sensor and a humidity sensor in order to control a room cooler and room heater or the air conditioners to thereby produce a comfortable indoor environment have been provided.
These prior-art air conditioners control an indoor temperature in response to a sensing signal from a contact type temperature sensor, e.g., a thermistor, placed in or near the body of the air conditioners. That is, the air conditioners only consider the temperature of air surrounding the temperature sensor as an average indoor temperature and controls the room heater and room cooler of the air conditioners.
The temperature which the body of an indoor person feels is the most important factor for controlling an indoor environment by means of air conditioners or room heaters and room coolers. The temperature of radiation heat which the skin of human body receives from an infrared radiant from interior surfaces of a room, contributes to the temperature which the body of the person feels in addition to the temperature of air in direct contact with the skin of the body of the person.
For example, heat radiant from a room heater, window arrangement, etc., produces a hot feeling on the human body, while a window arrangement and wall of a room that absorbs heat radiant from the human body produces the feeling of a bone-reaching chill. Thus, the prior-art method of controlling an environment in response to a single temperature output of the contact type temperature sensor such as the thermistor sensing air in contact with the sensor cannot provide a truly comfortable environment to a person.